1. Field of the Invention
The present invention relates to a facsimile apparatus which has a memory for storing image data in a facsimile receiver to shorten image data transmission time and allow an efficient image processing.
2. Description of the Prior Art
In a prior art facsimile apparatus, because of combined use of apparatus of different processing speeds, it is a common practice to match data processing speeds of a transmitter and a receiver prior to transmission of the image data in order to establish a communication channel. Since it is meaningless to transmit the image data at a transmission speed higher than the processing speed of a decoder or recorder in the receiver, it is a common method to adjust the transmission rate of the transmitter to comply with the processing speed of the receiver.
In the adjustment, a minimum transmission time defined in the CCITT (Consulting Committee of International Telegram and Telephone) Recommendation T30 is used as a reference. As described in the Recommendation, the minimum transmission time is a transmission time of one unit of code length (code length of one scan line for the facsimile apparatus).
The minimum transmission time is defined by the following reason. It is not difficult using a present data communication technique to transmit data at a transmission rate of 9600 bps while using an MH (modified Huffmann) encoding system which is common as a redundancy compression system. In this case, a minimum transmission time of 3-4 ms is possible. However, because old type or low cost machines having longer minimum transmission time are also used, the minimum transmission time is selected from 0 ms, 5 ms, 10 ms and 20 ms in the pretransmission procedure of the CCITT Recommendation in accordance with th processing capability of the receiver in order to assure the transmission compatibility so that the processing time of the receiver is assured.
In order to meet the requirement for the minimum transmission time and assure the processing time of the receiver, dummy bits are added to each line of code bits in the transmitter so that the transmission rate of one line does not exceed the processing capability of the receiver. This means that the telephone fee charged to the transmitter is higher due to the dummy bits if the receiver has a lower processing capability than the transmission capability of the transmitter.
In the present situation where the technology rapidly advances, it may be anticipated that the record speed of the receiver is faster than the transmission rate of the transmitter. In such a case, the faster unit should be operated to comply with the slower unit.
Thus, if the image data is transmitted in a manner to comply with the CCITT Recommendation, a device having a high transmission capability due to the advancement of the technology cannot perform with its full capability unless other devices have the same capability, or it can communicate with an old type or low cost device only at the low rate of the old type device.